Mobile communication terminals represented by cellular phones are widely used. In late years, a reduction in the size of the terminal is needed while the multiband of the terminal is advancing. For this reason, a reduction in the size of the duplexer employed in the terminal is also strongly needed. However, a reduced size of the duplexer may degrade the isolation between a transmission terminal and a reception terminal. Thus, the duplexer is required to reduce the size and improve the isolation.
Japanese Patent Application Publication No. 2006-180192 describes a technique where a ground pattern is provided for a partition between interconnections. Japanese Patent Application Publication Nos. 2006-80921 and 2006-66978 describe a technique where a surface acoustic wave (SAW) chip is mounted on an insulation substrate by flip-chip bonding and is sealed with a ring-shaped electrode formed on the insulation substrate.
The technique disclosed in Japanese Patent Application Publication No. 2006-180192 needs a large distance between the interconnection and the ground pattern. Thus, it may be difficult to obtain a sufficient isolation between the transmission terminal and the reception terminal. The ring-shaped electrode proposed in Japanese Patent Application Publication Nos. 2006-80921 and 2006-66978 may degrade the isolation.